Realm Update Deleting existing data - ios

Question

Using Swift 5 for iOS13.
I am trying to update an existing Realm record with a Contact Picker result. The function deletes all the object content except for the new content.
My code
class Person: Object {
#objc dynamic var personId = UUID().uuidString
#objc dynamic var firstName: String = ""
#objc dynamic var surname: String = ""
#objc dynamic var mobileNumber: Int = 0
#objc dynamic var password: String = ""
#objc dynamic var myContactID: String = ""
override static func primaryKey() -> String? {
return "personId"
}
}
extension HomeController: CNContactPickerDelegate {
func contactPicker(_ picker: CNContactPickerViewController, didSelect contact: CNContact) {
picker.dismiss(animated: true, completion: nil)
let person = Person()
let me = realm.objects(Person.self).filter("mobileNumber == %#", mobileNumber)
person.myContactID = contact.identifier
person.personId = me.first!.personId
try! realm.write {
realm.add(person, update: .modified)
}
self.viewWillAppear(true)
}
}
All the existing content of the Person class in the Realm database disappears except for myContactID and personID.

Answer 1

That is because you are updating the Person with new data.
The line let person = Person() creates a new instance with all the default values. (firstName: String = "" etc..)
So, when you assign myContactID and personId to this newly created person, it will look like this:
Person {
personId = FAE4C224-D37E-4C77-B6F1-C60A92F188D0;
firstName = ;
surname = ;
mobileNumber = ;
password = ;
myContactID = contactIdentifier;
}
And when you call realm.add(person, update: .modified), it will overwrite the record associated with the primary key with this newly created person.
You want to fetch an existing person and modify it. You can do something like this:
guard let me = realm.objects(Person.self).filter("mobileNumber == %#", mobileNumber).first else { return }
try! realm.write {
me.myContactID = contact.identifier
}